Revision as of 20:39, 4 June 2007

Contents

Introduction

The mission: Get MythTV to change channels on my Cable provided STB (Set Top Box). I connected a coax cable from the STB to my caputre card, but with an STB one cannot tune/change stations using the tuner built into the capture card. The capture card should remain on channel 3, and I need an Infra Red emitter to send signals to my set top box when Myth needs to change channels.

Hardware

You can build your own serial port IR emitter very inexpensively or you can buy one.

MyBlaster - $45 - $50 - Reportedly very easy to set up and use. It has long range. Does not use lirc. However it is a large item. Scripts for changing the channel on your box included in the Myth contrib directory and are available on SourceForge. Info and purchase here.

irblaster.info - $12 - $15 - inexpensive serial IR blaster similar to what you might build yourself. You stick it with included double sided tape right to the STB pointing at the STB's IR reciever.

Recommended IR Blaster HOWTOs

Andy's HOWTO is the easiest to follow, but is Fedora specific. It says Fedora Core 3, however I have used it on Fedora Core 4, and it should work for most Fedorae. It expects that Myth has been setup according to Jarod Wilson's Guide.

Installing the IR Blaster

Use the links at the bottom of this page for detailed instructions. You will plug one end of the IR Blaster into a serial port on the Myth backend, and the other side with the diode is pointed at the STB. Normally you put it right over the STB's IR eye as pictured below from Geoff Holden's blog.

You have to load lirc_serial at boot. There are instructions in the HOWto links. The way I do it on Fedora is to edit modprobe.conf. Since you likely also have an IR receiver, such as on the hauppage cards, you need two lirc modules loaded, the lirc_i2c module for the IR receiver, and lirc_serial for the IR emitter. Again please see the details instructions in the links above.

Once the modules are loaded, you run two instances of the lirc daemon lircd. One instance uses device /dev/lircd0 and the other /dev/lircd1.

Configuring Myth Backend

Instructions in the HOWTO links show you how to make a channel change script. You need to use MythTV setup to tell Myth to use the script to change channels.

Run the mythtvsetup by opening an X window console and typeing mythtvsetup.

Once you have defined your input connection, select it and find the following setup page:

You will enter the command for changing channels here. Note the box "Preset Tuner to channel" which says 3. This is important, just as your TV has to be set to channel 3 to recieve signals from the STB, so does your PVR card. Furthermore, I found that this did not work. In order to actually tune my PVR-250 to channel 3 I used this command in my rc.local, which runs after startup:

iv-tune -c 3 -d /dev/video1

to change the PVR 250 to channel 3.

MyBlaster setup -- does not require LIRC

If you prefer not to have to mess around with LIRC there are alternatives. One of these is the MyBlaster serial. (See the vendor list below.) It is a commercial product but the linux drivers are GPL. The latest driver can be found on SourceForge. To set up, simply edit the perl based driver script for your port and device and call the script using the external channel change script configuration option in mythtv-setup. It is that easy.

Troubleshooting

Note that MythTV sends frequency IDs to the external channel changer script and not the channel number. If you see some weird four/five digit numbers being sent through the IR blaster, you will need to go to the channel editor in setup and change the freqid for the channels to match the ones that you expect to receive through the IR blaster.

Note: You can get MythTV 0.20 to send out channel numbers as the parameter. First, get EPG working. Then using, mythtvsetup, channel-editor, remove all your channels. To add the channels again, this time, instead of scanning for channels, get the channel list from the epg service and readd those channels.

do not* be tempted to change the configure options to set COM1/IRQ4 in the pre-make configuration. Rather, follow the directions and pass those options through /etc/modules.conf or /etc/modprobe.d/aliases.

Changing the settings at the earlier stage will produce a module that conflicts with the standard lirc (and a frustrating string of errors in dmesg: ledxmit_dev: register_chrdev failed ledxmit_serial: Unknown symbol ledxmit_register_plugin).